What is causing it?

The java.lang.OutOfmemoryError: Out of swap space? is thrown by JVM when an allocation request for bytes from the native heap fails and the native heap is close to exhaustion. The message indicates the size (in bytes) of the allocation which failed and the reason for the memory request.

The problem occurs in situations where the Java processes have started swapping, which, recalling that Java is a garbage collected language is already not a good situation. Modern GC algorithms do a good job, but when faced with latency issues caused by swapping, the GC pauses tend to increase to levels not tolerable by most applications.

java.lang.OutOfMemoryError: Out of swap space? is often caused by operating system level issues, such as:

The operating system is configured with insufficient swap space.

Another process on the system is consuming all memory resources.

It is also possible that the application fails due to a native leak, for example, if application or library code continuously allocates memory but does not release it to the operating system.